Japanese laid-open publication (Tokukaihei) No. 3-207056 discloses a method of identifying the types of discs for optical disc devices using various types of optical discs. In this method, specific information signals (type identifying signals) recorded on the respective optical discs in advance are read out so as to identify various types of optical discs, more specifically to distinguish a music-use CD (compact disc) and a computer-use CD-ROM.
According to the method disclosed in the Japanese publication No. 3-207056, since information recorded on a disc is actually read out to identify the disc, it is possible to accurately identify the disc. However, in order to identify the type of disc, it is necessary to control the rotation speed of the disc to be a predetermined value and to control the focus servo and tracking servo when reading the information from the disc. Thereafter, by reading out information called "TOC" (table of contents) recorded in the innermost periphery section of the disc, the type of the disc is first identified. Then, the operation of a processing system is switched according to the result of the identifying process. Therefore, this method causes an increase in a so-called "starting time", that is the time taken from identification of the type of the disc to the completion of switching the operation of the device, including switching the processing system, performed after the identifying process.
Hence, in an optical disc device using various types of optical discs, even if the basic physical properties of discs, such as the signal frequency and recording density of the recorded information or the rotation speed and linear velocity, etc. of the discs, are substantially the same like in a music-use CD and computer-use CD-ROM, a long time and a number of processes are required to start the optical disc device.
In an optical disc device using various types of discs (for example, CD and DVD (digital video disc)), which are different from each other in their physical properties, particularly in the recording density and track pitch, to a greater degree than the degree of the difference between a music-use CD and a computer-use CD-ROM, it is often necessary to perform the process of switching an optical system of an optical pickup in order to obtain better signal reproduction characteristics in some cases. There also may be a possibility that there is a difference in the linear velocity, i.e., the rotation speed of the disc, between discs having different physical properties. In such a case, it is necessary to increase or decrease the rotation speed of the disc. Of course, the above-mentioned processes can only be carried out after identifying the type of a disc. As a result, it takes a long time to start the optical disc device.
As described above, with the prior art disclosed in the above-mentioned publication concerning an optical disc device for reproducing information recorded on various types of optical discs, a long time is required to identify the type of disc and an additional time-consuming process needs to be performed in accordance with the result of the identifying process. Thus, this technique suffers from a problem that the starting time of the optical disc device becomes longer.